Motion stages (XY tables and rotary tables) are widely used in various manufacturing, product inspection, and assembling processes. A common solution currently in use achieves XY (i.e. planar) motion by stacking two linear stages (i.e. a X-stage and a Y-stage) together via connecting bearings.
A more desirable solution involves having a single movable stage capable of XY (i.e. planar) motion, eliminating additional bearings. It might also be desirable for such a movable stage to be able to provide at least some Z (out of plane) motion. Attempts have been made to design such displacement devices using the interaction between current-carrying coils and permanent magnets. Examples of efforts in this regard include the following: U.S. Pat. Nos. 6,003,230; 6,097,114; 6,208,045; 6,441,514; 6,847,134; 6,987,335; 7,436,135; 7,948,122; US patent publication No. 2008/0203828; W. J. Kim and D. L. Trumper, High-precision magnetic levitation stage for photolithography. Precision Eng. 22 2 (1998), pp. 66-77; D. L. Trumper, et al, “Magnet arrays for synchronous machines”, IEEE Industry Applications Society Annual Meeting, vol. 1, pp. 9-18, 1993; and J. W. Jansen, C. M. M. van Lierop, E. A. Lomonova, A. J. A. Vandenput, “Magnetically Levitated Planar Actuator with Moving Magnets”, IEEE Tran. Ind. App., Vol 44, No 4, 2008.
There is a general desire to provide displacement devices having characteristics that improve upon those known in the prior art.
There is a general desire to estimate characteristics of the motion of such displacement devices. For example, there is a desire to estimate the position of (e.g. measure) the movable stage(s) of such devices relative to their stator(s). In some cases, there can be a desire to provide position estimation solutions that are independent of line of sight obstruction.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.